Projector screen calculator
How big a picture you'll get from where the projector sits, where to put it for the screen you have, and whether it will be bright enough. Metric and imperial side by side.
1How big will the picture be?
From 4.00 m (13 ft 1 in) with a 1.40–2.24 zoom lens, the projector's full 16:9 frame is 1.79–2.86 m wide (5 ft 10 in – 9 ft 4 in): smallest zoomed in, largest zoomed out.
| Shape | Width | Height | Diagonal |
|---|---|---|---|
| 16:9fills the frame | 1.79–2.86 m5 ft 10 in – 9 ft 4 in | 1.00–1.61 m3 ft 4 in – 5 ft 3 in | 81–129 in205–328 cm |
| 2.39:1letterboxed: bars above and below | 1.79–2.86 m5 ft 10 in – 9 ft 4 in | 75 cm – 1.20 m2 ft 5 in – 3 ft 11 in | 76–122 in194–310 cm |
| 4:3pillarboxed: bars at the sides | 1.34–2.14 m4 ft 5 in – 7 ft 0 in | 1.00–1.61 m3 ft 4 in – 5 ft 3 in | 66–105 in167–268 cm |
2Where should the projector go?
Put the lens between 3.10 m and 4.96 m from the screen10 ft 2 in to 16 ft 3 in
- Screen
- 100 in (254 cm) 16:9: 2.21 m × 1.25 m7 ft 3 in × 4 ft 1 in
- Projector frame needed
- 2.21 m × 1.25 m (16:9)
The projector's frame matches the screen exactly. Distances are from the front of the lens; check your projector's manual for where its maker measures from.
3Will it be bright enough?
231 cd/m² (nits) · 67.4 fL
- Compared with cinema
- 481% of SMPTE's 48 cd/m² (14 fL)
- Picture
- 100 in (254 cm) 16:9, 2.76 m² (29.7 ft²)
- Lumens for 48 nits here
- 416 lumens at gain 1
Brighter than the cinema reference: plenty for a dark room, with headroom for some stray light. Outdoors at dusk, or with lights on, the sky and lamps add light to the screen and wash out dark scenes, so the same picture looks dimmer: wait until it is properly dark, use a smaller picture or a brighter projector.
How it works
A projector's throw ratio is the distance from the lens to the screen divided by the picture width, so the width is the distance divided by the ratio: 4 m at 1.5 gives a picture 2.67 m wide. A zoom lens covers a range of ratios, and so a range of sizes and of places the projector can go.
The ratio describes the projector's full frame, usually 16:9. A 2.39:1 "scope" film inside it keeps the full width with bars above and below; a 4:3 film keeps the full height with bars at the sides.
Brightness spreads over the whole frame. At gain 1.0, foot-lamberts are the lumens divided by the area in square feet, and candela per square metre (nits) the lumens divided by π times the area in square metres; gain multiplies both. Cinemas aim for 48 cd/m² (14 fL) in a dark room. Treat the answer as a best case: accurate colour modes, eco modes and an ageing lamp all give less light than the spec sheet.
Sources
- Throw ratio = distance ÷ picture width, and zoom lenses spanning a range of ratios: Throw (projector), Wikipedia. Makers measure from slightly different points, so check your manual.
- Cinema reference luminance of 48.0 cd/m² (14.0 fL) at the centre of the screen, with a commercial-cinema tolerance of ±10.2 cd/m², and the note that luminance falls as lamps age: SMPTE ST 431-1:2006, D-Cinema Quality — Screen Luminance Level, Chromaticity and Uniformity.
- A perfectly diffusing surface lit by one foot-candle (one lumen per square foot) has a luminance of one foot-lambert, which is 1/π candela per square foot: Foot-lambert, Wikipedia. Conversions (1 fL = 3.426 259 cd/m², 1 ft = 0.3048 m, 1 in = 2.54 cm): NIST Guide to the SI (SP 811), Appendix B.9.
Questions
Where do I find my projector's throw ratio?
On its spec sheet or in the manual, often written as a range such as "throw ratio 1.40–2.24:1". If the maker only gives a distance for one screen size, divide that distance by the picture width.
What screen gain should I enter?
A matte white screen, a painted wall or a white sheet is close to 1.0. Grey screens are usually below 1, and high-gain screens 1.3 or more, which makes the picture brighter straight ahead but dimmer from the sides.
Is 2000 lumens enough for an outdoor movie?
It depends on the picture size and how dark it is. Enter your screen size in step 3: if the result is well above the 48 cd/m² cinema reference, it will look good once the sky is properly dark. At dusk the sky adds light, so start later or keep the picture smaller.